Alan O'Day died this Friday, May 17^th; he was 72 years old.

After a rough battle with cancer, "Undercover Angel" singer Alan O'Day died this Friday from brain cancer. Alan O'Day passed away at his home in Westwood, Calif, and shall be mourned by many, including Alan O'Day's dear friend and award-winning songwriter Diane Warren.

"My dear dear friend and mentor Alan O'Day has passed away. 'If you believe in forever, then life is just a one night stand. If there's a rock and roll Heaven, well you know they've got one hell of a band.' (From Alans' song Rock And roll Heaven). Well the band just got better. Rest in Peace my friend," grieved Diane Warren, according to The Hollywood Reporter.

Alan O'Day was best known for writing and singing "Undercover Angel," which was a smash hit in 1977. O'Day also co-wrote many songs for the children's show, "Muppet Babies" and wrote and performed music for the National Geographic Show, "Really Wild Animals."

O'Day wrote popular songs for many artists including Cher, the Righteous Brothers and Helen Reddy. Reddy's song, "Angie Baby" became a number one hit in 1974, which was written by O'Day.

Back in 1977, O'Day was the first artist signed to the new Warner Brothers label that was created for its composers that performed. It was here that O'Day released, "Undercover Angel," which ultimately sold 2 million copies.

O'Day is survived by his wife Yuka.

Even with brain cancer, O'Day's love of music and performing could not be exhausted.

"Alan continued to write and perform until his last days," a statement from 1st Phase Records reads according to The Hollywood Reporter. "Alan was a generous man who gave his heart and soul to the music industry."